The renal excretion and metabolism of the following compounds: choline, mono-, di-, tri-, methylamines, meperidine, dimethylaminoethanol and nicotinic acid are being studied using the isolated perfused rat kidney and the Sperber Technique in hens. The biphasic renal tubular transport of choline has been further described by micropuncture studies at various plasma choline levels. The effect of chronic ethanol treatment on plasma choline levels and on choline excretion is being evaluated. Excretion of three methylamines will be compared along with the ability of the kidney to perform methylation or demethylation reactions. Renal N-oxidation, a process that may contribute to the elimination of many endogenous compounds and pharmacological agents, is being currently studied using meperidine and trimethylamine as substrates. Other appropriate compounds will be investigated in this regard. The excretion of isoproterenol and its renal conversion to 3-0-methy 1-isoproterenol have been measured using a one pass, nonrecirculating system in the isolated perfused rat kidney. These studies are expected to demonstrate that the kidney plays a major role not only in the renal excretion of end products of metabolism but as a regulator of plasma concentration of choline and related aliphatic amines. This regulation occurs through filtration, reabsorption, metabolism and excretion in the kidney, the contribution of each process varying with plasma concentrations of the related compounds.